In recent years, a flexible display has been expected to be a next-generation display. The flexible display includes devices formed on a flexible substrate, such as an organic EL (Electronic Luminescence) and a TFT (Thin Film Transistor) for the drive circuit.
Meanwhile, the flexible substrate is not stable in shape and low in strength and thus it is not easy to form a device on the flexible substrate. Accordingly, it is underway to develop a method of manufacturing a flexible device by forming a flexible substrate on a support that is made of glass or the like that is stable in shape and high in strength, forming a device on the flexible substrate, and then releasing the flexible substrate and the device together as one unit from the support.
However, this method requires an excellent balance between (i) adhesiveness of the support with the flexible substrate and (ii) releasability of the support from the flexible substrate. That is to say, if the adhesiveness of the support with the flexible substrate is high, the releasability is low. In that case, it requires a strong force to release the flexible substrate from the support, and the strong force applied may break the device on the flexible substrate. On the other hand, if the adhesiveness of the support with the flexible substrate is low, the releasability is high. In that case, it is difficult for the device to be broken by the releasing, but it is difficult to form the device on the flexible substrate since the flexible substrate is not closely contact with the support and is unstable.
As described above, it is difficult to obtain a flexible substrate having, in good balance, both adhesiveness and releasability that are properties contrary to each other. The following documents disclose, as the means to solve the problem, a technology for providing a releasing layer between the support and the flexible substrate.
Patent Literature 1 discloses, as illustrated in FIG. 9A, a structure where a releasing layer composed of two layers is inserted between a support 201 and a flexible substrate 202. More specifically, a nitride layer 203 is formed on the support 201, and on the nitride layer 203, an oxide layer 204, the flexible substrate 202, and a device 205 are laminated in the stated order. The nitride layer 203 and the oxide layer 204 constitute the releasing layer. In this structure, the difference in film stress between the nitride layer 203 and the oxide layer 204 is used to release the oxide layer 204 and the flexible substrate 202 as one unit from the support 201 on which the nitride layer 203 has been formed, the releasing occurring at the interface between the nitride layer 203 and the oxide layer 204. Furthermore, the document discloses heating the interface by irradiating laser thereto, as one example of how to cause the releasing to occur.
Patent Literature 2 discloses, as illustrated in FIG. 9B, a structure where a releasing layer 213 is inserted between a support 211 and a flexible substrate 212, the releasing layer 213 being made of parylene or COC (cyclic olefin copolymer). More specifically, the releasing layer 213 is formed on a central portion of the support 211, but not on an outer circumferential portion of the support 211. The flexible substrate 212 is then formed to cover the releasing layer 213 and the outer circumferential portion of the support 211.
With this structure, the central portion of the support 211 has high releasability due to the releasing layer 213 that is present between the support 211 and the flexible substrate 212, while the outer circumferential portion has high adhesiveness since the support 211 and the flexible substrate 212 are in direct contact with each other without the releasing layer 213 therebetween. In this state, a device 214 is formed on a central portion of the flexible substrate 212. Subsequently, the outer circumferential portions of the support 211 and the flexible substrate 212, where they are in close contact with each other, are cut away. After this, the flexible substrate 212 is released from the support 211 at the interface between the support 211 and the releasing layer 213.